Knowledge of rock texture is often crucial in characterizing a hydrocarbon reservoir in an Earth formation. Rock texture, meaning the shapes and sizes of grains, the matrix and pore structure, for example, greatly effect porosity and permeability of the formation. Until now, knowledge of rock texture has been obtained through labor intensive studies based on core analysis. This analysis involves taking core samples of the formation, bringing the samples to the surface, then cutting or thin-sectioning the samples for examination under optical microscopes.
Currently, micro-resistivity measurements can provide an image of a borehole wall. See U.S. Pat. No. 5,038,378 to Chen, for example. Also, optical spectroscopic analysis can provide information about the borehole wall. See U.S. Pat. No. 4,994,671 to Safinya et al. for example. Television and still cameras have been proposed for viewing boreholes through transparent slugs of fluid using visible or near infra red light. See U.S. Pat. No. 2,953,979 to Rosene et al. Video cameras have been proposed for producing an image of a borehole wall or casing. See U.S. Pat. No. 5,134,471 to Gendron at al. and U.S. Pat. No. 5,140,319 to Riordan, for example. There exists a need, however, for a technique for imaging the borehole wall of an earth formation at an improved spatial resolution to further characterize rock texture of the borehole wall through formation fluids such as filtrate water, mud, and oil.